The present invention relates to a strut for MacPherson-type suspensions for motor-vehicles, of the type comprising an upper tubular member of sheet metal which forms the cylinder of telescopic shock absorber, and a sheet metal housing having an upper wall with a circular aperture, a lower wall with a hole for the attachment of one of the parts of a ball-and-socket joint of a suspension wishbone, a lateral end wall defining a flange for the attachment of a bearing bush or bearing spindle and a static part of a wheel brake, and a pair of opposing faces, a lower part of the tubular member being engaged in the circular aperture of the upper wall of the housing and fixed to the said housing by means of welding.
A structure of this type is known from the published French patent application No. 2,299,982.
In known struts for MacPherson suspensions the connecting member is usually formed by forged steel or cast iron. Parts of this type have the disadvantages of being expensive, not only because of the forging or casting operations necessary, but also, and above all, because of the subsequent finishing operations necessary on the forged or cast part. A further disadvantage is that a connecting member of steel or iron constitutes an unsuspended mass of considerable weight and is, therefore, undesirable.
The solution described in the French application No. 2,299,982, using a sheet metal housing, reduces both the costs of manufacture and the weight of the connecting member. Indeed, a housing of sheet metal may be made more economically and with a lighter weight than an equivalent member of forged steel or cast iron.
However, in the French application No. 2,299,982 the lower end of the tubular member is simply fixed in, and welded to the edge of, a circular aperture in the upper wall of the housing. This solution has the disadvantage of not ensuring a sufficient bending strength of the strut in relation to the housing. In fact, the bending forces which occur, in use, between the strut and the housing can produce undesirable elastic deformation of the upper wall of the housing, with consequent angular oscillations of the axis of the tubular member with respect to the predetermined, projected position of the axis. If the bending forces are very high, the upper wall of the housing may be permanently deformed, with a consequent permanent angular displacement of the axis of the tubular member with respect to its predetermined position. Furthermore, the welding which joins the lower end of the tubular member to the upper wall of the housing is subject to fatigue in use and may eventually break, with the possibility of serious accidents resulting from the actual collapse of the suspension of the vehicle.
These disadvantages are reduced by using sheet metal of considerable thickness (of the order of 10 millimeters) as seems to be apparent from the drawings of the French application in question. The use of very thick sheet metal reduces the advantages of cost and weight which could be achieved with the use of strong but thinner sheet metal, that is, with a thickness of the order of 3 to 4 millimeters.
British Pat. No. 988,503 illustrates and describes a strut for MacPherson suspensions in which the connecting member is formed by a strong piece of steel or cast iron which has the aforesaid disadvantages relating to cost and weight. The connecting member has a pair of upper and lower arms comparable to the upper and lower walls of a sheet metal housing. A circular aperture is bored in the upper arm and a circular seating is made in the lower arm. The lower part of the tubular member is engaged in both the aperture of the upper arm and the seating of the lower arm and is moreover brazed to the upper arm. This solution, as a result of the double engagement, effectively ensures a high bending strength of the tubular member with respect to the connecting member.
This solution is applicable to the connection of a tubular member with a connecting member of sheet metal and is mentioned in the published German patent application (Offenlegungsschrift) No. 25.14.456. In this application the tubular member is welded to the interior of a corresponding, sleeve-shaped part of a sheet metal connecting member. The same application provides for the possibility of making the sleeve part lighter by removing an intermediate portion from it. As a result of this removal the sleeve part is reduced to a pair of upper and lower bush portions which may be considered equivalent to the upper and lower walls of a sheet metal housing or to the upper and lower arms of the British Pat. No. 988,503. However, the German application in question does not provide for the axial support of the tubular member with respect to the sheet metal connecting member.
The provisions of both the British Pat. No. 988,503 and the German patent application No. 25.14.456 have the disadvantage that the tubular member extends through the full height of the connecting member. In the case of a suspension for drive wheels, this precludes the passage of a horizontal drive shaft through the connecting member, since the section of the tubular member which extends substantially vertically through the connecting member would interfere with the drive shaft.
A further disadvantage of these arrangements is that the presence of the lower end portion of the tubular member in contact with the lower aperture of the housing makes it impossible to assemble, inside the latter, a part (ball or spherical seating) of a ball-and-socket joint for the connection of the suspension wishbone. As is well known in many MacPherson-type suspensions, it is desirable to arrange this ball-and-socket joint as high up as possible, that is, as near as possible to the substantially horizontal axis of rotation of the wheel (insofar as this is allowed by the presence of a possible drive shaft, in the case of a drive wheel). By assembling the ball-and-socket joint very high up, a reduction is in fact, obtained in the moment arm of the stress forces in the connecting member, the length of this arm being equal to the distance between the axis of rotation of the wheel and the center of the ball-and-socket joint. In this way the housing and tubular member assembly is under less stress.
The present invention has the object of eliminating the said disadvantages by providing a strut for MacPherson-type suspensions with a low manufacturing cost and a low weight, due to making its connecting member or housing from strong, but not excessively thick, sheet metal, and in which, on the one hand, the connection between the tubular member and the connecting member is extremely resistant to bending forces and, on the other hand, the internal space of the housing is substantially free, for example, for the passage of a drive shaft or from the positioning of one of the members of a ball-and-socket joint.